1. Field of the Invention
The present invention relates to an inter-equipment data link system, and in particular, to an inter-equipment system for double data transmission equipments such as those in a dual system, a duplex system or the like.
In a recent computer system, in particular, in a recent social system, it is demanded that communications be performed using a high-level data-link control (hereinafter, abbreviated as HDLC) procedure as a data transmission/reception method. Further, in order to improve system reliability, data transmission/reception is performed between double data transmission equipments. For this purpose, the double data transmission equipments should have functions of data transfer between the double equipments, which data has been received in the HDLC procedure.
2. Description of the Related Art
FIG. 1 shows a block diagram of an inter-equipment data link system in the related art. In the figure, an A data transmission equipment 10A has an arrangement the same as that of a B data transmission equipment 10B. An HDLC unit 12A in the data transmission equipment 10A performs control of the HDLC procedure and has a line unit 13A and a monitor unit 14A. The line unit 13A performs data transmission/reception between the data transmission equipment 10A and another data transmission equipment via a line 16A for the HDLC. A signal received by the line unit 13A is supplied to an HDLC driver 18A from the HDLC unit 12A, and is branched by the HDLC unit 12A and supplied to the monitor unit 14A. The monitor unit 14A outputs HDLC data for monitoring it, which data is transmitted and received through the line unit 13A. The HDLC driver 18A determines, based on the contents of a control portion of a received HDLC data frame, whether the data frame is an I frame of an information transfer type. If it is determined that the data frame is the I frame, the HDLC driver 18A reports this determination to a data reception unit 20A. The data reception unit 20A inputs therein the contents of an information portion in the I frame from the HDLC driver 18A.
The contents input in the data reception unit 20A are supplied to a data decomposition unit 22A by which only a data portion is obtained from the contents of the information portion, the data portion being stored in a self-data region 25A in a memory 24A. A special output unit 28A, a CDT transmission unit 30A and a computer output unit 32A read data stored in the self-data region 25A, convert it to special control signals, data of a CDT (Cyclic Digital Telemeter) format, and data of a format for a computer, and outputs them, respectively.
Together with the operations described above, data stored in the self-data region 25A is edited in a HDLC format in an inter-equipment editing unit 34A. The edited data is transmitted to a line 41A via an inter-equipment data transmission and reception unit 36A, an HDLC driver 38A and a line unit 41A in an HDLC unit 40A. The line unit 41A performs data transfer with a line unit 41B in the B data transmission equipment 10B via the line 42. A signal received from the B data transmission equipment 10B in the line unit 41A is input in the inter-equipment data transmission and reception unit 36A from the HDLC unit 40A via the HDLC driver 38A. An inter-equipment decomposition unit 42A extracts only the contents of an information portion in an HDLC data frame which is input in the inter-equipment data transmission and reception unit 36A, and stores the extracted data in another data region 26A in the memory 24A.
When an essential line unit such as the HDLC unit 12A or the like stops functions thereof due to some trouble or the like for example, each of the special output unit 28A, CDT transmission unit 30A and computer output unit 32A switches a data region used and thus starts reading data from the other data region 26A in the memory 24A. Thereby, the special output unit 28A, CDT transmission unit 30A and computer output unit 32A output special control signals and data of the formats, respectively, based on data received from the B data transmission equipment 10B.
In the inter-equipment data link system in the related art, as described above, the HDLC procedure is used in the inter-equipment data link, that is, the data transfer between the data transmission equipments 10A and 10B. Extra times is required for data editing by the inter-equipment editing unit 34A, 34B and for data decomposition by the inter-equipment decomposition units 42A, 42B. Therefore, as the amount of data handling increases, a delay in data processing and/or load increase in data editing and decomposition operations may occur.
Thus, an amount of data transferred between the data transmission equipments 10A and 10B forming the duplex system may increase and thereby an amount of data processing delay may increase. As a result, when the HDLC units 12A or the like stop operation due to some trouble for example and as a result a data region used is switched from the self-data region 25A to the other data region 26A, the latest data may have not yet been stored in the other data region. If such a situation occurs, non-latest data stored in the other data region 26A is read and thereby the special output unit 28A, CDT transmission unit 30A and computer output unit 32A output erroneous data.